My blood sugar level changes much. Why?

  I checked my blood sugar level twice, today. First, in the morning, before going for a walk, it was 270, which was very high. Then, right after the walk, it was 93, which was very low. What means this fluctuation in my blood sugar levels?  On March 1st, when I went to the hospital, I had to take glucose sugar before being seen by the doctor, because my blood sugar level was as low as 60. Why?
  When I was walking along the Tomakomai river, I was very glad to find pussy willow blossoms beginning to come out. "Spring is just around the corner," I felt.